The present invention relates in general to controlling the posture of sheets being conveyed, and in particular to a method and apparatus for adjusting the posture or position of sheets being fed to a portion such as a printing station in a printer.
In such apparatus as a laser beam printer, there is a type of apparatus in which a large number of stacked sheets are held and the sheets are fed, one at a time, to a predetermined position such as a printing station. When the sheets are conveyed, they must be in a predetermined posture so that an intended operation such as printing can be performed correctly. Sheets however are prone to be brought into incorrect postures while being conveyed; for example, they may be skewed. Therefore, devices for controlling the posture of sheets being fed are used.
Japanese laid-open patent application No. 100047/1983 discloses a device including a stationary checking member which is arranged such that fed sheets will collide against the member and their skewed posture can thereby be corrected. Specifically, upon collision each sheet is brought into a posture in which its leading edge is correctly positioned, and possible skewed postures of sheets being fed may thus be corrected.
Japanese laid-open patent application No. 190144/1984 discloses another device for correcting the skewed posture of fed sheets in a manner similar to that in which the device of the previously mentioned publication does. This device further comprises a sensor for detecting the thickness of sheets, for instance, by means of transmitted light therethrough, for the purpose of achieving optimum correction of skewed posture of sheets being fed. The force acting between a checking member and a sheet colliding against the checking member is adjusted by controlling the force for conveying the sheet depending on the detected thickness of the sheet.
Further, Japanese laid-open patent application No. 90343/1982 proposes a device for registering sides of sheets being fed. The device comprises a side registration guide. Each fed sheet is once turned aside so that a front corner thereof will not collide against the guide while being conveyed, and subsequently its direction of travel is again turned so as to bring a side of the sheet into contact with the guide, thereby positioning the sheet.
Another device is also known in which a corners or a side of each sheet is directly brought into contact with a guide without being once separated therefrom in order to register the sides of the sheets.